Mercruise 5.0 lossing speed not rpm

[peter555]

after running for 20 min on my merc 5.0 with B1 at RPM 3000 to 3200 for 15 to 20min A humming sound from the engine. Loss of speed no loss of rpm. Shift to neutral for a minute shift back and runs good for the next 10 minutes then repeat.
checked the prop at a shop no problem there. same problem w/my other prop. No problems at 2000 rpm. I have no mercruiser dealer near by. need help on what can it be.

 

[alldodge]

Either spun a engine coupler or spun a prop hub, my guess is the coupler.
Did you smell any burning rubber?

 

[Scott06]

Cone clutch not grabbing fully ?

 

[peter555]

I know is not the prop because the RPM stays at 3200. How do I check for the spun coupler or the clutch?

 

[alldodge]

The engine coupler is metal inner and outer and is filled with rubber between the two. If the coupler tears, then rubber starts burning and the engine rpm stays up, but the drive shaft coming out of the coupler slows down and with that the prop.

The prop is made the same way. There is a metal spline inserted into a rubber hub, and the hub is pressed into the prop

 

[rickasbury]

sounds like one or the other...when my coupler went out, it went out! Leaning more to the prob hub alldodge ?

 

[alldodge]

sounds like one or the other...when my coupler went out, it went out! Leaning more to the prob hub alldodge ?

Agree, only because there is no mention of burning rubber. Normally the coupler goes first because folks don't do their maintenance

 

[peter555]

hello everyone to close this case and after a year finally had to drag the boat to a Mercruiser dealer in Miami and replace the entire middle housing. problem solved.
thank u evryone.

 

[nola mike]

I know is not the prop because the RPM stays at 3200.

Old post...

MOD EDIT: Peter is the OP, so it is OK.

 

[peter555]

after running for 20 min on my merc 5.0 with B1 at RPM 3000 to 3200 for 15 to 20min A humming sound from the engine. Loss of speed no loss of rpm. Shift to neutral for a minute shift back and runs good for the next 10 minutes then repeat.
checked the prop at a shop no problem there. same problem w/my other prop. No problems at 2000 rpm. I have no mercruiser dealer near by. need help on what can it be.

By the way I drove 104 miles to my nearest Merc I/O and they traced the problem to the crown bearing and the entire middle housing. End of problem